The mother of a child who fell into a gorilla pit in a US zoo, which led to the animal being shot dead, has spoken out, saying “accidents happen.” Meanwhile, the case has sparked a wave of criticism from both animal rights activists and parents.

Cincinnati Zoo visitors were shocked on Saturday to see an unattended four-year-old boy climb through a series of barriers and fall into a gorilla enclosure.

As seen in a video captured by terrified onlookers, the inhabitant of the enclosure, a 180-kilogram 17-year-old Western Lowland gorilla named Harambe, grabbed the boy and dragged him by the ankle for several meters. Two female gorillas in the enclosure complied with calls from zoo-keepers to leave the cave, but Harambe stayed.

The boy was inside the gorilla cave for well over 10 minutes before being rescued after the animal was shot dead by zoo-keepers.

While for some it seemed as if the animal was protecting the child, the sight of the boy’s head banging on the concrete floor while being dragged through the enclosure led to the decision to shoot Harambe, according to the zoo’s director, Thayne Maynard.

“The gorilla was clearly agitated. The gorilla was clearly disoriented. Looking back, we would make the same decision,” Maynard told a news conference on Monday.

The zoo also released a statement saying: “We are heartbroken about losing Harambe, but a child’s life was in danger and a quick decision had to be made.”

The child’s mother, Michelle Gregg reportedly attempted to defend herself in a Facebook post that she later deleted.

“God protected my child until the authorities were able to get to him. My son is safe and was able to walk away with a concussion and a few scrapes [...] no broken bones or internal injuries.

As a society we are quick to judge how a parent could take their eyes off of their child and if anyone knows me I keep a tight watch on my kids. Accidents happen […],” Gregg wrote, as cited by several media outlets.

Nevertheless, animal rights activists and social media users mobilized on Monday to express their outrage over the killing of a representative of an endangered species. Some 270,000 people signed online petitions to protest the shooting, some of which called on police to hold the child’s parents accountable.

An endangered animal should not have had to pay with its life because of a lack of supervision #CincinnatiZoo#Harambe

Maynard explained, however, that tranquilizing Harambe was not even considered because “tranquilizers do not take effect for several minutes and the child was in imminent danger. On top of that, the impact from the dart could agitate the animal and cause the situation to get much worse.”

“They made a tough choice and they made the right choice because they saved that little boy’s life,” Maynard added.

Many social media users have defended the zoo-keepers’ decision, saying the animal’s reaction would have been hard to predict and the child’s life was, in fact, at stake.

Yes, I agree the mother is to blame for not watchin' the child in the first place but that gorilla could have easily killed that child.

Animal rights activists held a vigil for the killed primate two days after the tragic event, while campaigners have gathered outside the zoo while holding signs and placards to say their goodbyes to Harambe. They have also called for a demonstration to be held on June 5 to protest the decision to kill him.

On Tuesday, Hamilton County Prosecutor Joseph Deters announced that the Cincinnati Police Department would indeed look into what happened at the zoo.

"The incident at the Cincinnati Zoo involving the young child who fell into the gorilla enclosure is under investigation by the Cincinnati Police Department," he said in a statement. "Once their investigation is concluded, they will confer with our office on possible criminal charges. When the investigation and review are complete, we will update the media."

The US Department of Agriculture will also investigate after the Cincinnati-based Stop Animal Exploitation NOW filed an official complaint. The agency's Animal and Plant Health Inspection Service told the AP that it will "be looking into this incident."